Fly-by-wire systems in aircraft, as opposed to mechanically controlled systems, use electronic signals to control the flight surfaces and engines in the aircraft. For example, instead of having the pilot controls mechanically linked to the control surfaces via a hydraulic system, the pilot controls are electronically linked to a flight computer, which, in turn, controls flight surface actuators via electronic signals. By further interfacing the flight computer to aircraft sensors, sophisticated control algorithms may be used to provide autopilot functionality, as well as to stabilize and control the aircraft.
While fly-by-wire systems have become commonplace in commercial and civilian fixed wing aircraft, their adoption among rotorcraft, such as helicopters, has been much slower due, in part, to the increased complexity of controlling and stabilizing a rotorcraft. However, by adopting fly-by-wire systems in helicopters, safer operation may be achieved in difficult flight environments such as low speed, low altitude, degraded visual environments and inclement weather. Another area in which fly-by-wire systems may benefit rotorcraft is in the reduction in pilot workload. By providing automated features such as stabilization in response to wind, control axis decoupling, position hold and heading hold functionality, the pilot is freed up to focus on the environment in which he flies.
One challenge in the design of fly-by-wire systems for rotorcraft is maintaining control of the rotorcraft during sudden changes in the acceleration of the rotorcraft caused by wind gusts or by sudden pilot control settings. For example, in circumstances when the flight computers control the speed of the rotorcraft, sudden changes in acceleration of the rotorcraft may cause instability when the speed control loop has high loop gains, or may cause speed errors when the speed control loop has lower loop gains.